A quick Google search shows that the 21AP is a rotary impact head. The RB impacts that I am familiar with can easily be adjusted to any degree of circle you wish, and by simply flipping the wire trip upward will operate full circle. The distance they will throw is regulated by adjusting a screw the the water stream passes. I have not actually seen this model, but I have to believe it would be similar.

Guys thanks for the information. I figured out that you have to take a small band off the sprinkler while it is on. Once you have that you push down on the sprinkler head and twist it 90 degrees until you find tha pattern you want. It was rather easy once I figured that out. Thanks for the help!